The present invention relates to a safety device for a fluid production well, of the type comprising:                a valve housing intended to be fixed tightly inside a fluid flow conduit, the housing delimiting a fluid flow passage and comprising:                    a valve used to seal the passage, and which can move between an open position of the passage and a closed position of the passage;            means for permanently biasing the valve towards its closed position; and            means for connecting the housing to a coupling member for a working wire line intended to move and anchor the housing in the conduit;                        means for holding the valve in the open position against the permanent biasing means, said holding means comprising at least one movement element for the valve, which can move in the valve housing between a rest position and an active valve biasing position, and an element for permanently returning the movement element to its rest position; and        means for hydraulically actuating the holding means, which can be controlled by a control signal to actuate the holding means upon receipt of a valve open control signal by the actuating means, and to deactivate the holding means in the absence of said signal.        
Such a device is used to secure a well for the production of oil or another fluid (notably gas, vapour or water), in particular when said well is eruptive and can be sealed rapidly in case of failure of the surface installation, said failure producing the disconnection of the open control signal.
A device of the above-mentioned type is known from U.S. Pat. No. 4,002,202, said device being lowered in a production casing of an oil well by means of a working wire line. Said device comprises a valve housing, a rod for holding the valve in the open position and electromagnetic coils for actuating the support rod. The coils are fixed to the outside of the casing at a determined point thereon on, and are connected electrically to the surface by electric cables.
When an electric control signal is received by the electromagnetic coils, the valve is held in the open position by the support rod, against a return spring.
In the absence of a control signal, the return spring is deployed to move the rod, which allows rapid sealing of the valve.
A safety device of the same type is also known, driven by a hydraulic control line extending outside the casing from the surface.
Such devices are not entirely satisfactory. The safety device must be positioned at a determined point of the well, opposite the actuating coils, and the coils must be connected to the surface by electric power supply lines, or must be positioned opposite the inlet of the hydraulic conduit.